The role of amino groups in the structure of Parathyroid hormone will be studied. Preliminary data suggest that the N-terminal amino group of bovine PTH is buried and this interpretation will be further examined. Experiments on the accessibility of the N-terminal group in oxidized PTH will also be conducted. Attempts to prepare N-abbreviated peptides, 2-84 and 3-84 PTH will be made and the accessibility of the N-terminus in these peptides determined. Biological activity of these peptides will also be measured. The accessibility of the lys amino groups in PTH will be studied. If an inaccessible lys is observed its exact position in the peptide chain will be determined. Further examination of the position of basic residues in the tertiary structures of PTH will be conducted by mild trypsin digestion. Preliminary data with this approach suggest that certain basic residues may be more accessible than others. The location of such accessible basic residues will be determined. Using a cleavable amino-group cross-linking reagent (DTPB) the proximity of lys residues in the N-terminal domain to those in the C-terminal domain will be tested. These data will provide more information on the structure of PTH which will allow better understanding of many of the chemical and biological properties of this hormone.